Method of producing crimped viscose fibers

ABSTRACT

Crimped regenerated cellulose fibre is made from viscose by submitting freshly spun filaments emerging from a conventional spinning bath to a stretch equal approximately to one third of the total stretch to be imparted, while the filaments still substantially consist of cellulose xanthate and while they are still in the plastic state, conducting the partly stretched filaments through an acid bath for their further though not yet complete transformation into cellulose hydrate, subjecting them either in, or outside, this bath to a second stretching which corresponds to the difference between the initial stretch and the total stretch, and then, after substantially completely transforming the filaments into staple lengths, immersing the staple lenths in a hot water or alkaline bath, and finally submitting them to conventional after-treatment. Preferably the partially stretched filaments are 70-95% converted to cellulose hydrate prior to the second stretch, which may be carried out in an aqueous sulphuric acid bath.  Preferably, also, the viscose has a ratio of alkali to a -cellulose of below 0.9, e.g. 0.8-0.85. The total stretch of the fibre may correspond to 60-65% of its original length.  An example is given.  Specification 499,671 is referred to.

Sept. 25, 1962' F. KAISER METHOD OF PRODUCING CRIMPED VISCOSE FIBERS Filed July 51, 1957 snare The present invention relates to a new method of producing crimped viscose fibers, and more particularly to a method of producing crimped viscose fibers from freshly spun viscose whereby a high degree of crimping is obtained.

Various processes for producing crimped viscose fibers are known. The basic features of the known processes is that the freshly spun fiber is subjected to a more or less strong stretching, if necessary in various stages, and in this manner more or less completely freed from the precipitating liquid. The stretched and more or less acidfree fibers are then cut into staple fibers and upon working up in loose conditions the fibers show a more or less permanent crimping.

It is well known that the degree of crimping depends upon numerous factors such as the degree of ripeness of the viscose, the composition of the spinning bath, the temperature of stretching of the fibers and other conditions. However, prior to the present invention there has been no clear perception as to why in certain cases a good crimping is obtained, that is the fibers are sharply bent, and in other cases only a weak degree of crimping is obtained, that is the arc length of the crimped fiber is many times the desired arc length.

It is therefore a primary object of the present invention to provide a method of producing crimped regenerated cellulose fibers from viscose wherein there is an assurance that the finally obtained fiber will be highly crimped.

It is another object of the present invention to provide a method of producing crimped regenerated cellulose fibers by stretching the freshly spun viscose during the conversion of the cellulose Xanthogenate to regenerated cellulose.

It is still another object of the present invention to provide a method of producing highly crimped regenerated cellulose fibers from viscose by subjecting the freshly spun viscose fibers to a series of stretching operations during conversion of the freshly spun viscose to regenerated cellulose.

Other objects and advantages of the present invention will be apparent from a further reading of the specification and of the appended claims.

With the above objects in view, the present invention mainly consists in a method of producing crimped regenerated cellulose fibers from viscose by subjecting freshly spun viscose fibers to a predetermined stretch, according to which method the freshly spun viscose fibers still in plastic state and consisting in this state mainly of cellulose xanthogenate is subjected to a first or pre-stretch corresponding at most to one-third of the total of the predetermined stretch, subjecting the thus partially stretched viscose fiber after partial conversion of the same to cellulose hydrate to a second stretch corresponding to the difference between the first stretch and the total of the predetermined stretch so as to further stretch the fiber, and completing conversion of the thus further stretched fiber to regenerated cellulose, whereby the thus obtained regenerated cellulose fiber is highly crimped.

It has been found in accordance with the present invention that by maintaining the other conditions constant, the degree of stretching of the freshly spun fibers during their coagulation and conversion to cellulose hydrate or regenerated cellulose as well as the stage during this conversion that the stretching is carried out has a considerable influence on the crimping of the finally obtained fibers.

It has been found that if the freshly spun fibers leaving the precipitation bath, which fibers are mainly still in the cellulose Xanthogenate condition, and in which condition the fibers are still plastic, are subjected to a very strong degree of stretching corresponding to 50% or more of the total degree of stretching to which the fibers are subjected, the degree of crimping of the finally obtained fibers is not always satisfactory.

It is necessary in accordance with the present invention in order to obtain a high degree of crimping with assurance that the results obtained can always be repeated to subject the freshly spun viscose fibers coming from the precipitation bath while while still in plastic conidtion, that is while still consisting mainly of cellulose Xanthogenate because the acid of the precipitation bath has not yet had time to convert the cellulose xanthogenate to cellulose hydrate to any considerable degree, to only a relatively slight stretch which corresponds in this state to at most one-third of the total stretch to which the fibers are to be subjected. Subsequently, after the fibers have been partially converted from cellulose Xanthogenate to cellu lose hydrate, but not yet completely converted to cellulose hydrates, i.e. -95% of the original cellulose Xanthogenate has been converted to cellulose hydrate, the thus partially converted fiber-s are subjected to the remaining stretch either in a single stretching operation or in a plurality of stretching operations. This further stretching of the partially converted fibers must be carried out before the fibers have been completely converted to cellulose hydrate because after complete conversion of the fibers to cellulose hydrate a strong degree of stretching will result in tearing of the fibers.

It is preferred in accordance with the present invention that the further stretching of the partially stretched fiber, that is the stretching of the fibers after partial conversion of the same to mainly cellulose hydrate is about double the pre-stretching or stretching of the fibers while the same are mainly in the form of cellulose Xathogenate. Most preferably the total amount of stretching of the fibers is to an extent such that the stretched fiber is about 60-65% of the thickness of the original fiber before stretching. In other words, the total amount of stretching is such that the diameter of the original fiber is reduced so as to be between 6065% of the original diameter. In accordance with the present invention up to one-third of the stretching is carried out in the pre-stretched step when the fiber is mainly in the form of cellulose xanthogenate, that is up to one-third of the total reduction in diameter, or up to about 12-13% of the diameter reduction occurs during the first stretching step while the remaining twothirds of the total diameter reduction, or 24-26% of the diameter reduction occurs in the second stretching operation when the fiber is partially converted to cellulose hydrate.

After the final stretching, that is after the fiber has been stretched so that the diameter of the fiber is between 6065% of the diameter of the original fiber the fiber is finally completely converted into the form of regenerated cellulose or cellulose hydrate. The resulting fiber is highly crimped.

The freshly spun fiber emerging from the sulfuric acid spinning bath upon emerging starts to be changed from cellulose Xanthogenate into cellulose hydrate. This conversion however requires a relatively long period of time, this being due partly to the formation of a cellulose skin about the fiber in the sulfuric acid bath which hinders the penetration of the acid into the inner portion of the fiber, the penetration being slower if the skin is thicker. It is thus clear that when it is stated herein that the fiber during the first stretching operation is in xanthogenate condition it means that the fiber is substantially or in the main in the form of cellulose xanthogenate.

The time that the fiber remains in the spinning bath is not sufficient under any circumstances to substantially convert the fiber into the form of cellulose hydrate. The stretching is accomplished in accordance with the present invention by withdrawing the fiber from the spinning bath at a predetermined speed, for example at a speed of 40 m./ minute. The fiber is then drawn onto a second roller at a greater speed, for example at a speed of 50 m./ minute. This increase of speed between the first and second roller results in a stretching of the fiber, and this stretching is the first or pre-stretching while the fiber is still mainly in the form of cellulose xanthogenate. After the fiber has to a great extent been converted to cellulose hydrate, for example 75-95% of the original cellulose xanthogenate has been converted to cellulose hydrate, this being accomplished if necessary by passage of the pre-stretched fiber through a second bath, the fiber is then withdrawn on a third roller at a still greater speed, for example at a speed of 65 m./minute to accomplish the final stretching, e.g. the remaining two-thirds of the predetermined stretch. Since the length of the fiber remaining in the first precipitating bath from which the fiber is spun is about 10-15 cm. generally, and assuming a Withdrawing speed of the fiber of about 60 m./minute, it is apparent that the fiber moves about 1 meter per second so that the fiber emerging from the original spinning bath has remained in the spinning bath only about one-tenth of a second. This is of course insuflicient to completely convert the cellulose xanthogenate into cellulose hydrate and that is why it can be stated that during the first stretching operation the fiber is mainly in the form of cellulose xanthogenate.

After emerging from the spinning bath there is practically no further conversion of the cellulose xanthogenate into cellulose hydrate because the acid still remaining on the fiber becomes very quickly exhausted. Therefore, the fiber is passed into a second acid bath in accordance with the present invention to further convert the cellulose xanthogenate to cellulose hydrate, though not yet completely, and after emerging from this second acid bath the fiber which is now partially converted to cellulose hydrate is, in accordance with the present invention, subjected to the final stretching operation to stretch the remaining two-thirds of the predetermined stretch, that is to stretch it so that the thickness of the fiber is reduced the final 24-27% to a thickness which is about 6065% of the thickness of the original fiber.

In accordance with a preferred embodiment of the present invention this final or after stretching is preferably carried out in an acid medium in which the acid content amounts to about 10 g. per liter of H 80 This acid content can easily be arrived at by treating the freshly spun fiber or cable of fibers, which still contain certain amounts of acid from the precipitating bath, with measured amounts of hot water during this final stretching operation. A temperature of 50-100 C. of the hot water is particularly suitable.

It is known that in order to obtain a good degree of crimping that a relatively unripe viscose having a Hottenroth degree of ripeness of 14 or about should be used. The alkali content of the viscose plays a decisive role for obtaining such degree of ripeness. In accordance with the present invention it is preferred to utilize a viscose which has an alpha cellulose content of above 8.5 and preferably in the range of 8.8-9%, while the alkali content is preferably below 7.5, though preferably not below 7.0%. A viscose of this type of which the alkali factor (that is the relationship between the NaOH and the alpha cellulose) is below 0.9, and preferably is between 0.8 and 0.85 is particularly suitable for crimping in accordance with the method of the present invention.

In accordance with the present invention the precipitating baths are of the same type and composition as the usual precipitating baths, baths with a sulfuric acid content of more than 100 g./l. of sulfuric acid and high sodium sulfate content of more than 300 g./l. with the addition of small amounts of zinc salts being preferred.

The fibers which in accordance with the present invention have been subjected to a first stretching operation while the fibers are mainly in the form of cellulose xanthogenate and to a second stretching operation while the fibers are partially converted to cellulose hydrtae are, after practically complete conversion to cellulose hydrate or regenerated cellulose, without any particular further tension conducted to a cutting device in which the fibers are cut and then finally in loose condition subjected to the usual final treatment. Preferably, the cut fibers are immediately dropped into a hot treating bath, this first treating bath being as usual an alkali bath. The use of such bath is not essential for obtaining the desired crimping since by properly stretching the fibers in accordance with the present invention the crimping can finally be obtained by introducing the cut and stretched fibens into a bath of only hot water. After this suspending operation the fibers are subjected to the customary after treatment such as desulfurization, washing, bleaching, brightening and drying of the finally cut fibers which are obtained at the end of the preferably continuous process in a condition which, with respect to crimping, closely corresponds to natural wool fibers.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its details and method of operation, together with additional objects and advantages thereof, will be best understood from the following description of the accompanying drawings in which the drawing schematically illustrates an apparatus for carrying out the method of the present invention.

Referring now more particularly to the drawing, the viscose solution flowing in through the conduit 1 through the nozzle 2 into the spinning bath 3 which is contained in the spinning vat 4- is formed into fibers at the nozzle and these fibers are drawn from the bath by means of a roller 5 which, for example, rotates at a speed such that the peripheral speed is 40 m./minute. The distance between the nozzle 2 and the roller 5 is about 15 cm. The fresh fiber 6 from the roller 5 is wound about a roller 7 which runs at a peripheral speed of about 48 m./minute. The fiber is wound several times around this roller 7 and for this purpose is passed over a glass fiber conductor 8. From the roller 7 the fiber is passed into a hot stretching bath 9, which bath is heated by means of heating devices which are not shown so that the bath is maintained at a temperature of preferably C. The acid bath liquid is passed into the vat 9 through the inlet 10 and out of the same through the outlet 11. In order to keep the fibers 6 immersed in the stretching bath glass fiber guides 12 and 13 are arranged at the beginning and the end of the bath respectively. The fiber emerging from the bath 9 is conducted over a three member roller arrangement consisting of rollers 14, 15 and 16 which run with a starting peripheral speed of 53 m./minute. The rollers serve partly to squeeze out the excess bath liquid from the fiber. The spray nozzles 17 which are arranged above the rollers 14, 15 and 16 serve the same purpose and the nozzles run hot water over the rollers. The liquid running over the rollers is caught in trough 18 and can be utilized for example in the stretching bath trough 9.

The prewashed fibers are then passed to a second three roller arrangement consisting of rollers 19, 20 and 21 which run at a starting peripheral speed of 65 m./minute, and the fibers are here again pressed. From these rollers the fiber is passed into a cutting machine 22. In this machine the fibers are cut into the desired lengths. The still wet cut fibers fall into the bath 23 which is filled with dilute sodium hydroxide and has the effect of neutralizing the fibers, this bath being maintained at a temperature of 95 C. by means of heating arrangements which are not illustrated. The final working up of the fibers =by bleaching, washing and drying can be carried out in the normal manner.

The following example which should be read in conjunction with the above description of the attached drawings will further illustrate the method of the present invention. The scope of the invention is, of course, not meant to be limited to the specific details of the example. In the example the change in the thickness of the fiber is given by relationship to the change in deniers. It is understood that a fiber has a denier value of one denier when 9000 meters of this fiber weighs 1 g. Thus, if 9000 meters of the fiber weighs 2 g. the fiber has a denier value of 2 denier, etc. The absolute thickness in millimeters is not given because of the extremely small absolute thickness, for example a fiber having a denier value of 3 deniers actually has a diameter of 0.017 mm. It is for this reason that the fiber thickness is given in relationship to the denier value thereof.

Example A viscose containing 8.9% alpha cellulose and 7.3 NaOH and having a degree of ripeness according to Hottenroth of 15 is spun in a bath which contains 120-135 g. of H 80 about 340 g. of Na S and 5-10 g. of ZnSO per liter. The fiber is drawn from the bath at a speed of 40 m./minute and while still mainly in the form of cellulose xanthogenate is by means of .a correspondingly faster running roller drawn at a rate of 47-50 m./ minute. The fiber drawn from the spinning bath has a denier value of about 5 denier. After being drawn onto the second roller at the faster Speed and thereby somewhat stretched the fiber has a denier value of about 4 denier.

The fiber is then passed through an intermediate bath containing -30 g./l. of H 80 per liter of hot water, the temperature of the bath being between 50-l00 C., and the bath also containing a small amount of salt. The fiber is drawn onto a three roller arrangement moving at a peripheral speed of 60-65 m./minute. The fiber is first sprayed with Water and is then passed over a second three roller arangement moving at a starting peripheral speed of 65 m./minute whereby the fiber is drawn and without tension passed into a cutting device. The fiber which is passed into the cutting device has a final denier value of about 3 denier. The still acid fiber is then cut into the desired lengths and the cut fibers fall into a bath containing about 0.1-0.15 g./l. of NaOH and which is maintained at a temperature of 90- 100 C. The fibers coming from the bath are then subjected in the usual manner to washing, bleaching, brightening and drying. The resulting fibers are crimped and with respect to the crimping have the appearance of natural wool.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, there-fore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a method of producing crimped regenerated cellulose fibers from viscose by subjecting freshly spun viscose fibers to a predetermined stretch corresponding to a reduction in the diameter of the fiber to between 60- 65% of the original diameter, the steps of subjecting a viscose fiber emerging from a sulfuric acid precipitating bath containing more than g./l. of sulfuric acid and more than 300 g./l. of sodium sulfate and being still in plastic state and consisting mainly of cellulose Xanthogenate to a first stretch corresponding to about onethird of the total of said predetermined stretch; converting about 75-95% of the original cellulose Xanthogenate to cellulose hydrate in an acid bath so as to form a partially stretched, partially converted fiber; subjecting the thus partially stretched, partially converted fiber after said conversion of about 75-95% of the or1ginal cellulose xanthogenate to cellulose hydrate to a second stretch corresponding to the difference between said first stretch and the total of said predetermined stretch; completing conversion of the thus further stretched fiber to regenerated celluose; cutting the thus obtained fiber of regenerated cellulose into fiber segments; and treating the thus obtained fiber segments in a hot bath so as to obtain highly crimped fiber segments of regenerated cellulose.

2. In a method of producing crimped regenerated cellulose fibers from viscose by subjecting freshly spun viscose fibers to a predetermined stretch corresponding to a reduction in the diameter of the fiber to between 60- 65 of the original diameter, the steps of subjecting a viscose fiber having a ratio of alkali'to alpha cellulose of 0.8-0.9 and emerging from a sulfuric acid precipitating bath containing more than 100 g./l. of sulfuric acid and more than 300 g./l. of sodium sulfate and being still in plastic state and consisting mainly of cellulose xanthogenate to a first stretch corresponding to approximately a 12-13% reduction in the diameter of the original fiber; converting about 75-95% of the original cellulose xanthogenate to cellulose hydrate in an acid bath so as to form a partially stretched, partially converted fiber; subjecting the thus partially stretched, partially converted fiber after said conversion of about 75-95% the original cellulose xanthogenate to cellulose hydrate in said acid bath to a second stretch corresponding to a further reduction in the diameter of the fiber to a diameter which is about 60-65% of the diameter of the original fiber; completing conversion of the thus further stretched fiber to regenerated cellulose; cutting the thus obtained fiber of regenerated cellulose into fiber segments; and treating the thus obtained fiber segments in a hot bath so as to obtain highly crimped fiber segments of regenerated cellulose.

3. A method of producing crimped regenerated celluose fibers from viscose, comprising the steps of spinning viscose fibers in a sulfuric acid precipitating bath containing more than 100 g./l. of sulfuric acid and more than 300 g./l. of sodium sulfate and withdrawing the thus freshly spun fibers from said bath at a first predetermined speed onto a first take-up means; further drawing said fibers from said first take-up means while said fibers are still in plastic state consisting mainly of cellulose xanthogenate onto a second take-up means at a second predetermined speed greater than said first predetermined speed and adapted to stretch said fibers to an extent corresponding to a reduction in diameter of said fibers to about /3 of a reduction to a final diameter of 60-65% of the original diameter of said fibers; converting about 75-95% of the original cellulose xanthogenate to cellulose hydrate in an acid bath so as to form a partially stretched, partially converted fiber; further drawing said partially stretched, partially converted fibers from said second take-up means after said conversion of about 75-95% of the original cellulose xanthogenate to cellulose hydrate through said acid bath onto a third take-up means at a third predetermined speed greater than said second predetermined speed and adapted to stretch said fibers to an extent corresponding to a further reduction in the diameter of said fibers to a final diameter of 60-65% of the original diameter; completing conversion of the thus stretched fibers having said final diameter to regenerated cellulose; cutting the thus completely converted stretched regenerated cellulose fibers into fiber segments; and treating said fiber segments in a bath so as to obtain crimped fiber segments of regenerated cellulose having a high degree of crimping corresponding to natural Wool.

4. In a method of producnig crimped regenerated cellulose fibers from viscose by subjecting freshly spun viscose fibers to a predetremined stretch, the steps of subjecting a viscose fiber still in plastic state and emerging from a sulfuric acid precipitating bath containing more than 100 g./l. of sulfuric acid and more than 300 g./l. of sodium sulfate and consisting mainly of cellulose Xanthogenate to a first stretch corresponding to about one-third of the total of said predetermined stretch; converting about 75-95% of the original cellulose Xanthogenate to cellulose hydrate in an acid bath so as to form a partially stretched, partially converted fiber; subjecting the thus partially stretched, partially converted fiber after said conversion of about 7595% of the original cellulose xanthogenate to cellulose hydrate to a second stretch in said acid bath corresponding to the difference between said first stretch and the total of said predetermined 23 stretch; completing conversion of the thus further stretched fiber to regenerated cellulose; cutting the thus obtained fiber of regenerated cellulose into fiber segments; and treating the thus obtained fiber segments in a hot bath so as to obtain highly crimped fiber segments of regenerated cellulose.

References Cited in the file of this patent UNITED STATES PATENTS 1,930,803 Harrison Oct. 17, 1933 2,302,971 Moritz Nov. 24, 1942 2,340,377 Graumann Feb. 1, 1944 2,364,273 Cox Dec. 5, 1944 2,369,191 Thurmond Feb. 13, 1945 2,427,993 McLellan Sept. 23, 1947 2,440,057 Millhiser Apr. 20, 1948 2,515,834 Nicoll July 18, 1950 2,515,889 Nicoll July 18, 1950 2,723,900 Hooper Nov. 15, 1955 FOREIGN PATENTS 570,159 Great Britain June 25, 1945 

1. IN A METHOD OF PRODUCING CRIMPED REGENERATED CELLULOSE FIBERS FROM VISCOSE BY SUBJECTING FRESHLY SPUN VISCOSE FIBERS TO A PREDETERMINED STRETCH CORRESPONDING TO A REDUCTION IN THE DIAMETER OF THE FIBER TO BETWEEN 6065% OF THE ORIGINAL DIAMETER, THE STEPS OF SUBJECTING A VISCOSE FIBER EMERGING FROM A SULFURIC ACID PRECIPITATING BATH CONTAINING MORE THAN 100 G./1. OF SULFURIC ACID AND MORE THAN 300 G./.1 OF SODIUM SULFATE AND BEING STILL IN PLASTIC STATE AND CONSISTING MAINLY OF CELLULOSE XANTHOGENATE TO A FIRST STRETCH CORRESPONDING TO ABOUT ONETHIRD OF THE TOTAL OF SAID PREDETERMINED STRETCH; CONVERTING ABOUT 75-95% OF THE ORIGINAL CELLULOSE XANTHOGENATE TO CELLULOSE HYDRATE IN AN ACID BATH SO AS TO FORM A PARTIALLY STRETCHED, PARTIALLY CONVERTED FIBER; SUBJECTING THE THUS PARTIALLY STRETCHED, PARTIALLY CONVERTED FIBER AFTER SAID CONVERSION OF ABOUT 75-95% OF THE ORIGINAL CELLULOSE XANTHOGENATE TO CELLULOSE HYDRATE TO A SECOND STRETCH CORRESPONDING TO THE DIFFERENCE BETWEEN SAID FIRST STRETCH AND THE TOTAL OF SAID PREDETERMINED STRETCH; COMPLETING CONVERSION OF THE THUS FURTHER STRETCHED FIBER TO REGENERATED CELLOSE; CUTTING THE THUS OBTAINED FIBER OF REGENERATED CELLULOSE INTO FIBER SEGMENTS; AND TREATING THE THUS OBTAINED FIBER SEGMENTS IN A HOT BATH SO AS TO OBTAIN HIGHLY CRIMPED FIBER SEGMENTS OF REGENERATED CELLULOSE. 